1. Field
The present application relates generally to the operation and design of wireless devices, and more particularly, to the operation and design of wireless transmitters.
2. Background
There is an increasing demand to have wireless devices capable of low power operation to provide extended talk times. One key to achieving lower power consumption is associated with the performance of the device's transmitter. For example, it is desirable to have a transmitter for use in a wireless device that utilizes power very efficiently thereby extending talk times.
Typically, transmitters used by devices operating on wireless networks have a very wide dynamic range requirement (i.e., >75 dB). For example, in a multiple access wireless communication network, if all devices transmit at a high power level (i.e., limited dynamic range), for instance to provide greater coverage area per base station and thereby reduce costs, the signals transmitted from devices closer to the base station will be received with much higher signal strengths and will overpower signals transmitted from devices further away from the base station. Therefore, a wide dynamic range is required so that devices in communication with a distant base station can transmit at higher transmit powers than devices closer to the same base station. By controlling the transmit power of the devices based on their proximity to the base station, it is possible for the base station to receive the transmitted signals with approximately equal power levels, thereby providing the highest throughput for all devices.
When transmitting at very high output power (i.e., 4 dBm) the transmitter has to satisfy stringent linearity requirements. When transmitting at low output power (i.e., −55 dBm) the transmitter is constrained by the need for good local oscillator (LO) leakage and image suppression. When transmitting at medium output power (i.e., −8 dBm) the transmitter should consume as little battery current as possible to extend talk times. For example, in typical network implementations, the numbers and locations of the base stations are determined so that the medium power range happens to be the “most probable” power range used for voice calls.
Unfortunately, existing transmitters used in wireless devices are not very efficient at the medium and low output power ranges. It is therefore desirable to have a more efficient transmitter for use in wireless devices.